In the art of loading dock leveler apparatus, there have been several efforts to develop mechanisms for actuating the hinged extension member or so-called "lip" mounted on the distal end of the leveler ramp to place the lip in its working position for engagement with the loadbed of a truck or other vehicle. Typically, when the dock leveler ramp is raised to an inclined position preparatory to engaging the vehicle loadbed, the extension member or lip is moved from a pendant position to an extended position to serve as part of the leveler ramp surface.
One problem associated with prior art dock levelers pertains to the substantial actuating forces required to extend the lip member when the dock leveler ramp is raised to an inclined position. When the ramp is moved to an inclined position and the lip member is to be moved from its pendant position to its extended position the location of the center of gravity of the lip member with respect to its pivot connection to the ramp changes in such a way that substantial actuating forces are required to move the lip member to its extended position. This problem is aggravated by the need to provide, depending on the application of the dock leveler, lip members of varying widths and, accordingly, weights.
Although many prior art dock levelers include lip extension mechanisms with counterbalance springs associated therewith to assist in moving the lip to its extended position, heretofore the counterbalance mechanisms of prior art dock levelers have not been suitable for compensating for the increase in the actuating forces required to extend the lip member during raising of the ramp or to adequately compensate for lip members of different sizes and weights. Accordingly, it has been necessary to provide prior art dock levelers with ramp actuator devices which are of greater power capacity and strength than is desired, just to provide the capability of extending the lip member when the ramp is raised to its inclined position.
Still further, it has been considered desirable to provide a mechanism for actuating the lip which will maintain the lip in its extended position preparatory to engagement with the vehicle loadbed but also release the lip to decline to its pendant position once the vehicle has pulled away from the dock leveler. Positive mechanical latching mechanisms are desirable as compared with hydraulic dashpot or retarder mechanisms in that the latter type of mechanism is sensitive to substantial temperature variations which may be encountered in outdoor installations of loading dock levelers.
The present invention overcomes the above-mentioned problems with prior art dock leveler lip actuating mechanisms and provides additional desired features which will be appreciated by those skilled in the art.